In nuclear power plants, independent shut-down and safe-operation systems are dedicated to monitoring plant operation and evaluating numerous safety-related parameters. In the event one or more measured parameters indicate the existence of an unsafe condition, the shut-down system and/or the safe-operation system can automatically effect the appropriate remedial action. It is imperative that these safety control systems, known as plant protection systems, operate reliably, and accordingly, it is imperative that all measured and sensed parameters be valid.
In the context of nuclear plant protection systems, it is not uncommon to measure a multitude of parameters related to plant operation. These parameters include, for example, temperatures, pressures, flow rates, power density, neutron flux, fluid levels, etc. Other functions of the plant protection system include the status-monitoring of various components including valves, pumps, motors, control devices and generators.
Additionally, the plant protection system, under certain defined conditions, may initiate a reactor trip (RT), i.e., the rapid, controlled, and safe shut-down of the reactor by actuating various field systems and remote actuation devices. In the case of a pressurized light water reactor, the shut-down is often accomplished by the lowering of moderating control rods into the reactor core to cause the reactor to become sub-critical.
In co-pending U.S. application Ser. No. 08/848,556 noted above, an invention for use in the nuclear industry is disclosed for providing an Automatic Self-Testing system for remote sensors utilizing multi-sensor, multi-channel redundant monitoring and control circuits. The system senses or measures a parameter by a plurality of independent and sensor specific processing paths, each of which is provided with parallel redundant sub-paths that can each be sequentially inserted into the processing path to effect normal processing or be disassociated from the processing path to effect testing. Each sensor provides, either directly or indirectly, a digital value to a comparator which compares the measured value with a predetermined value that is, in turn, provided to coincidence logic that evaluates the output of its comparator with the input of the comparators of the other processing paths to provide an output indicative of a pass/fail condition. That invention advantageously provides an automatic self-testing system for verifying both the signal path processing functions and the validity of various logic states in parameter sensing systems, particularly parameter sensing systems using multiple redundant processing paths.
In copending U.S. Provisional Application Ser. No. 60/048,922, noted above (the contents are incorporated by reference herein), an invention for use in the nuclear industry is disclosed for providing a Digital Plant Protection System (DPPS) that utilizes digital signals and which has a greater mean time between failure. The DPPS is characterized by a plurality of cross-connected sensed-parameter processing channels that provide a suitably conditioned digital value to a digital comparator that tests the conditioned digital value against a pre-determined value to determine whether or not the sensed-parameter has been exceeded. A comparator is associated with each of the plural channels and receives a separate measurement of the sensed parameter for each channel. If a sensed-parameter is determined to be out-of-specification on a two-out-of-four basis, a `trip` signal is generated to effect remedial action.